1. Field of the Invention
The present invention relates to a bifocal camera and a camera with a zoom lens capable of changing focal length of a photographic lens system to permit the user to switch the photographic lens system for a plurality of focal length states to choose, for example, between a standard focal length state and a long focal length state or between a wide angle state and the standard state.
2. Description of the Prior Art
A photographic optical system employed with a bifocal camera as noted above is known, for example, from Japanese patent applications laid open under Nos. 59-42513 and 59-67511. A construction for shifting a main lens component back and forth along an optical axis is also known. In the known constructions, a main lens holder shiftable back and forth along guide grooves parallel to the optical axis is urged by a spring to a forward position, and is shifted back and forth through engagement with a gear rotatable by a rack and motor mounted adjacent the main lens holder. A special stopper mechanism is also provided to stop the main lens holder at predetermined positions (as disclosed in a Japanese patent application laid open under No. 57-146231, for example).
This known construction, however, requires the special stopper mechanism noted above and therefore even a stopper release mechanism to release a stopping action of the stopper mechanism prior to actuation of the motor, rendering the construction very complicated. The prior construction has a further disadvantage of being troublesome in operation since the stopper release mechanism must be manually operated prior to the actuation of the motor for shifting the main lens holder.
Furthermore, according to the known construction the motor is stopped only when the main lens component reaches one of the predetermined positions for the first or second focal length state.
With the known construction, therefore, the motor continues to receive an electric current for locking the motor even when the shifting of the main lens component is forcibly interrupted by some obstacle. This causes an undue force acting on a drive mechanism for shifting the main lens component as well as overheating of the motor, which result in damage to the camera.
In a further example of prior art construction a cam and cam follower combination is employed for pivoting an auxiliary lens component between an operative position on a photographic optical path and a retracted position off the photographic optical path (as disclosed in a Japanese patent application laid open under No. 59-17540).
This prior construction has the problem that, since the cam is defined on a pivotable member supporting the auxiliary lens component, its cam surface inevitably has a steep incline. In other words, the auxiliary lens support member is primarily for supporting the auxiliary lens component and therefore has a small axial dimension. Since the cam is defined on the support member having a small axial dimension, its cam surface must be steep thereby requiring a great force for pivoting the auxiliary lens component and shifting the main lens component axially which is detrimental to smooth pivoting of the auxiliary lens component. Such an inconvenience could of course be avoided by elongating the auxiliary lens holder in the axial direction, but then the entire camera must be long in the axial direction which is contrary to compact designing of the camera.
A lens barrier covering the front face of the main lens component is also known but conventionally it is used only with a monofocal camera incapable of focal length switching. A device for opening and closing the barrier is mounted adjacent the photographic lens assembly.
If, however, such a prior art construction is applied at it is to a bifocal camera with the main lens component shiftable over a considerable length in the axial direction, the portion surrounding the main lens compenent must be massive and heavy and imbalance in shape and weight of the entire camera becomes notable particularly when the main lens component is shifted to a front position. Besides, since the device for operating the lens barrier is also shiftable axially, it is difficult to utilize this device for operating other elements such as for vertically shifting a flash unit.
To eliminate these disadvantages the barrier operating device may be mounted in a main body of the camera and interlocked with the barrier, but then the interlocking mechanism must have a great length since the main lens portion including the lens barrier is moved over a great axial length. It is also necessary to absorb an amount of backward shifting of the main lens component and this renders the interlocking mechanism even more complicated.
With the bifocal camera, various devices such as a lens shifting device and an aperture device shift axially together with the main lens component. It has been one of the problems of the bifocal camera how power of a drive device mounted in the camera body should be transmitted to these driven devices.
In order to solve this problem a prior art construction has a drive gear mounted in a camera body and operatively connected to a lens drive device, a hollow rotary shaft integral with the drive gear and defining an axial groove, an inner shaft mounted in the hollow shaft to be slidable relative thereto and including a pin in engagement with the groove, and a gear fixed to a forward end of the inner shaft and operatively connected to a lens shifting device (as disclosed in a Japanese patent application laid open under No. 58-202431).
Such a prior art construction has a disadvantage of assembling inconvenience in that after fitting the inner shaft into the hollow shaft the pin must be fixed to the inner shaft with the pin placed in engagement with the groove of the hollow shaft. Furthermore, when the main lens component is shifted forward, the inner shaft is shifted so that a greater part thereof projects from the hollow shaft leaving only a small overlapping between the two shafts. This overlapping part lies in an intermediate position far from the lens drive device in the camera body and the lens shifting device as well. Therefore, the two shafts must be supported with great precision in order to avoid an inclination therebetween which would hamper smooth power transmission.
Furthermore, a bifocal camera wherein an automatic focus adjusting motor is movable in unison with shifting of a main lens component along the optical axis is known, for example, from a Japanese patent application laid open under No. 59-46610. However, this application does not disclose how the motor is connected to an electric circuit fixed to a camera body, leaving room for improvement.
With a camera such as a bifocal camera having a lens shiftable along the optical axis, it is necessary to render a light interrupting structure flexible along the optical axis for preventing entry of harmful light from positions between the movable lens and a photographic aperture.
A known light interrupting structure of this type comprises a flexible bellows mounted between a lens barrel and an exposure aperture (as disclosed in a Japanese utility model application laid open under No. 59-68327). However, the flexible bellows has a considerably large outer diameter when folded, and this permits no other components to be attached adjcent the bellows. Therefore the camera as a whole tends to be bulky presenting a serious problem to compact designing of the camera. Since such a bellows plays no part in attaching security of the lens barrel, some reinforcement must be provided for improved strength.